In the case where projection nuts having projections for welding, for example, are fed from a parts feeder, the projection nuts are arranged in a certain orientation of surface or back face before going out of the parts feeder. However, there are cases where the parts are fed out upside down for some reason or another and, to prevent them from being fed in a wrong state, a control method is known which consists in detecting the height of the parts and letting pass normal parts only while stopping unusual ones.
In the case where the two sides are discriminated based on the height of the parts conveyed, control may be easy if there is an appreciable difference in height between the parts looking upward and those looking downward but, if the difference in height is inappreciable, it is necessary to delicately adjust the space in height of the member which regulates the parts. For example, a projection nut generally has projections for welding formed at 4 corners of a square nut, and the quantity of protrusion in the direction of height of each projection is comparatively small while, in the direction of breadth, a quantity of protrusion larger than that in the direction of height is set. Therefore, in the case where the two sides are discriminated based on the height of parts, fine adjustment of the regulating member is rather difficult and even a slight deviation of adjusted value may make the discrimination impossible, thus letting pass parts which are placed upside down. Moreover, in the case of parts having hardly any difference in height between the upward looking state and the downward looking state, it is simply impossible to perform any control of passage based on the parts height.